An LCD has the advantages of portability, low power consumption, and low radiation. Therefore, the LCD has been widely used in various portable information products, such as notebooks, personal digital assistant (PDA), video cameras, and the like. Furthermore, the LCD is considered by many to have the potential to completely replace cathode ray tube (CRT) monitors and televisions.
In general, an LCD includes a gate driver and a data driver. The gate and data drivers drive thin film transistors (TFTs) of an LCD panel of the LCD to display images on a display screen of the LCD panel. Usually, an external power supply provides an operating voltage to enable the gate driver and the data driver to function. When the LCD operates, much electric charge is stored at the gate driver and the data driver. When the LCD is powered off, the electric charge stored at the gate driver and the data driver cannot discharge quickly. That is, the voltage at the gate driver and the data driver only drops slowly. As a result, it is difficult to rapidly shut off the TFTs. Therefore when the LCD is powered off, a voltage from the data driver is still applied to source electrodes of the TFTs, and this produces a so-called residual image on the display screen of the LCD panel.
For the purpose of eliminating residual images, it is common to provide a resistance between a power supply terminal of the gate driver and ground. When the LCD is powered off, the electric charge stored at the gate driver can be discharged quickly through the resistance. That is, the voltage on the gate driver drops quickly and the TFTs connected to the gate driver are shut off as soon as the LCD is powered off. Therefore the voltage from the data driver is not applied to the drain electrodes of the TFTs, and residual images are reduced or eliminated.
However, when the gate driver operates, there is current flowing through the resistance. This increases the power consumption of the LCD.
What is needed, therefore, is a discharge circuit and a liquid crystal display employing the discharge circuit that can overcome the above-described deficiencies.